Caption: Scanning electron micrograph (SEM) of a nitrogen- fixing bacterium, Rhizobium leguminosarum, on the root hair of a pea plant, Pisum sativum. Rhizobium is a free-living soil bacterium for most of its life, but at times forms a symbiotic association with the roots of leguminous plants. In return for breaking down atmospheric nitrogen & converting it into a form the plant can use, the bacterium gains access to the plant's carbohydrate food stores & is kept safe in the plant's tissue. Magnification: x9285 at 35mm size, x65,000 at 8x10-inch size.